2d vs 3d finite element analysis of free span response in subsea pipelines

Free-span formation in subsea pipelines, often caused by seabed irregularities, local scour, or differential settlements, poses a significant threat to pipeline integrity through the induction of vortex-induced vibrations (viv), fatigue damage, and potential structural failure. while two-dimensional (2d) numerical models are widely used in early-stage designs due to their simplicity and computational efficiency, their ability to accurately predict the complex dynamic behavior of pipelines remains limited. in contrast, three-dimensional (3d) models provide a more realistic representation of seabed geometry, pipe-soil interaction, and hydrodynamic loading, albeit at the expense of greater computational resources. this study presents a comparative numerical analysis of subsea pipelines with free spans under both 2d and 3d finite element models using abaqus software. key parameters, including deformed shapes, natural frequencies, and simulation run-times, are extracted and evaluated. the results offer valuable insight into the accuracy and applicability of simplified 2d models for preliminary design purposes, providing engineers with a practical framework for selecting appropriate modeling strategies based on project constraints and performance requirements. the study also lays the groundwork for aligning simplified numerical analyses with international design standards.